Sealing ring for a swinging yoke hydrostatic unit

ABSTRACT

An improved sealing ring for a hydrostatic transmission having a sideface with an irregular shaped chamfered portion such that when pressure reversal occurs within a hydrostatic transmission the seal will immediately shuttle across the mounting groove of the hydrostatic transmission by preventing a uniform extrusion within the clearance space between the manifold of the hydrostatic transmission and the yoke of the hydrostatic transmission.

BACKGROUND OF THE INVENTION

This invention relates to a sealing system for a swinging yoke hydrostatic unit. Swinging yoke hydrostatic units are very well known in the art as can be seen in U.S. Pat. No. 6,203,283 to Fleming et al. and the U.S. Pat. No. 6,257,119 to Ryken et al. The prior art utilizes a sealing system in its trunnion and manifold that utilizes three seals. Fluid cavities within the trunnion are spaced apart from one another and represent two separate hydraulic fluid lines. Prior art teaches the sealing of these two fluid cavities by using three seals to prevent fluid from these passages from seeping out of the fluid cavities or in between the fluid cavities. This three seal arrangement has proven problematic.

The area of deficiency in the three seal arrangement is related specifically to the center seal. During operation of the swinging yoke hydrostatic unit the pressure in the fluid cavities fluctuates, causing a significant difference in the pressure between the two cavities. Because of this fact, the cavity containing high pressure fluid transitions between the cavities. Thus, the center seal is required to shuttle from one side of the seal mounting groove to the other depending upon which cavity contains the high pressure fluid. Currently in the art, to handle this shuttling back and forth within the mounting groove, seals are designed to have radial grooves on their sideface to facilitate the infusion of pressurized fluid against the side of the seal and into the area where the seal energizer ring is located to hasten the movement of the seal across the groove. Simultaneously, the radial grooves on the opposite side of the seal facilitate the evacuation of fluid from the seal cavity as the seal moves across the groove. Unfortunately, because of the current design, when used, the seal material will flow to form a uniformly extruded lip in the clearance area between the hydrostatic transmission manifold and the swinging yoke and thus, will effectively seal the path that pressurized fluid must flow to generate the required force to cause the seal to shuttle to the other side of the mounting groove. Consequently, when the seal fails to move, pressure builds upon the seal and eventually the seal can no longer hold back the high pressure and the seal is lifted and thus, a leak path between the high pressure and low pressure side of the hydrostatic loop is created. This condition of the seal being thrust out of the area between the yoke and the housing and lifted thus allowing for the leak is known as “blow-by”.

There is a need in the art to provide for an improved seal design that alters the flow of the seal material such that a uniform extrusion will no longer be created between the manifold and the yoke so that “blow-by” does not occur within the hydrostatic transmission. Thus, it is a primary object of the present invention to provide a seal for a hydrostatic transmission that alters the sideface of the seal to disrupt the flow of the seal into a uniform extrusion and thus, improves upon the state of the art.

Yet another object of the present invention is to provide a seal that will immediately shuttle from one side of a mounting groove to another while maintaining a leak proof seal on the sealing surface when a pressure reversal within the hydrostatic transmission occurs.

These and other objects, features, or advantages of the present invention will become apparent from the specification and claims.

BRIEF SUMMARY OF THE INVENTION

The present invention is an improved sealing system for a hydrostatic transmission. The sealing system utilizes an improved seal that is to be placed in a mounting groove of the manifold and is in sealing contact with the swinging yoke trunnion of a hydrostatic transmission. The improved seal has a sideface with a chamfered portion therein and has an irregular shape. The irregular shape can be created by placing a notch in the chamfered portion or by cutting the sideface to form a different angle for the chamfered portion in relation to the sideface. Thus, when pressure reversal within the hydrostatic transmission occurs, the seal will immediately shuttle to the opposite side of the mounting groove and the seal will not flow to create a uniform extrusion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective assembly view of a bent axis unit equipped with the sealing system of this invention. Portions have been cut away to expose the sealing system;

FIG. 2 is a perspective view of the yoke of this invention;

FIG. 3 is a sectional view of one embodiment of this invention wherein the chamfered portion of the seal has a notch therein;

FIG. 4 is a sectional view of another embodiment of the present invention wherein the sideface of the ring is cut such that the chamfered section of the sideface is present at a new angle; and

FIG. 5 a sectional view of another alternative embodiment wherein a notch is placed within the manifold of the hydrostatic transmission thus allowing for the seal to be unaltered.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the swinging yoke hydrostatic unit 10 that has a yoke 11 pivotally installed in the housing 12 of a bent axis unit 14 having a main shaft 16. The housing 12 also has a manifold 17. A rotatable cylinder block kit 18 varies (and thereby the fluid displacement of the unit 14 varies) as the yoke 11 is pivoted by servo means 20 with respect to the housing 12 and the main shaft 16.

The yoke 11 has a central bucket portion 24 adapted to swingably carry the cylinder block kit 18 of the bent axis unit 14. The yoke 11 also includes a trunnion bearing portion or arm 22 for swinging control on one side of the bucket portion 24 and a trunnion 26 for fluid porting on the other side of the bucket portion 24.

The trunnion 26 has a pair of fluid passages or conduits 28 and 30 that intersect the running surface 32 in the area 34. The conduits 28 and 30 extend separately and are entirely within the bottom wall 36, the side wall 38, and the trunnion for fluid porting 26. One of the fluid conduits 28, 30 normally carries high pressured fluid (in the range of 0-550 BAR) when the cylinder block kit 18 rotates in one direction. Meanwhile, the other of the fluid conduits 28, 30 normally carries relatively low pressure fluid, such as control or charge pressure (in the range of 0-25 BAR). Of course, the normal pressures of the bent axis unit 14 may vary, depending upon the system requirements. The invention is applicable to other system pressure requirements with only minor modifications.

The conduits 28, 30 extend across the bottom wall 36 of the yoke 11. Then the conduits 28, 30 extend upwardly within the side wall 38. Near the top of the yoke 11, gauge ports 40, 42 can be provided. The gauge ports 40, 42 extend into the yoke 11 adjacent to the open top 44 so that they intersect the fluid conduits 28, 30 respectively. The fluid conduits 28, 30 curve and extend into the trunnion 26 for fluid porting.

The sealing system of the present invention can be seen as seals 46, 48, and 50 located on the manifold 17 adjacent to the trunnion 26. Each seal is disposed within a seal mounting groove 54. For convenience, only seal 48 will be discussed. Seal 48 is located on the exterior side of conduit 28 and on the interior side of fluid conduit 30 thus, representing a center seal. One should appreciate that seal 48 seals fluid from fluid conduits 28 and 30 thus preventing fluid communication therebetween.

Mounting groove 54 is disposed within the manifold 17 around the yoke trunnion 26 and has a top or outer surface 56 with an inner open end 58. Disposed within the mounting groove 54 is an energizer ring 60 that contacts the outer surface 56 and functions to force the seal 48 against the yoke trunnion 26. Additionally, the space between the yoke trunnion 26 and the manifold 17 forms a clearance space or fluid conduit 62 therebetween.

The seal 48 can best be seen in FIG. 3. The seal 48 has a recessed top surface 64 that receives the energizer ring 60. The bottom of the seal 66 is ribbed to facilitate sealing and movement. Additionally, the seal 48 has first and second sidefaces 68 and 70 respectively. The sidefaces 68 and 70 both have a chamfered portion 72 and 74 respectively. The chamfered portions 72 and 78 are of an irregular shape. For example, as shown in FIG. 3 notches 76 and 78 are cut into the chamfered sections 72 and 74 of the sidefaces 68 and 70. FIG. 4 shows an alternate embodiment wherein the chamfered portions 72 and 74 are cut such that a space 79 is formed between the sidefaces 68 and 70 when the sidefaces are in sealing engagement with the groove 54 thus, preventing a uniform extrusion. In another embodiment as seen in FIG. 5, notches 80 and 82 are placed within the manifold adjacent the seal.

In operation, all of the modifications to the seal and manifold as seen in FIGS. 3, 4, and 5 will cause the same result. When there is a pressure reversal within the hydrostatic transmission, the seal 48 immediately transitions from one side of the mounting groove 54 to the other. The notches 76, 78, 80 and 82, as well as the space 79 prevent a uniform extrusion in the fluid cavity 62. This allows the seal 48 to avoid “blow-by” and consequently improves upon the state of the art. Therefore, all of the objectives of the present invention have been met.

It will be appreciated by those skilled in the art that other various modifications could be made to the device without the parting from the spirit in scope of this invention. All such modifications and changes fall within the scope of the claims and are intended to be covered thereby. 

1. A sealing system for a swinging yoke hydrostatic unit having a housing with a yoke trunnion swingably mounted in a bore therein adjacent a manifold comprising: a conduit within the trunnion and being fluidly connected to the manifold; and a seal disposed within the manifold and around the trunnion located adjacent the fluid conduit, the seal having an irregular chamfered sideface portion.
 2. The sealing system of claim 1 wherein the hydrostatic transmission is a bent axis hydrostatic transmission.
 3. The sealing system of claim 1 wherein the seal has a top surface with a recess that receives an energizer ring.
 4. The sealing system of claim 1 wherein the seal has a bottom surface that is ribbed.
 5. The sealing system of claim 1 wherein the seal is within a mounting groove that is in the manifold and disposed around the trunnion.
 6. A seal for a hydrostatic transmission having a housing with a yoke trunnion swingably mounted in a bore therein adjacent a manifold comprising: a resilient body having a top, a bottom, and sidefaces having irregular chamfered sideface portions.
 7. The seal for a hydrostatic transmission of claim 6 wherein the top of the seal is formed to have a recess.
 8. The seal for a hydrostatic transmission of claim 6 wherein the bottom of the seal has a ribbed surface.
 9. A sealing system for a swinging yoke hydrostatic unit having a housing with a yoke trunnion swingably mounted in a bore therein adjacent a manifold comprising: a conduit within the trunnion and being fluidly connected to the manifold; at least one mounting groove within the manifold disposed around the yoke and located adjacent the fluid conduit; a notch disposed within the manifold adjacent the mounting groove; and a seal disposed within a mounting groove and in fluid communication with the notch. 